1. Field
The invention is concerned with the field of wheels and relates more particularly to a semi-hollow tire and an associated wheel rim, notably for agricultural machinery.
It relates chiefly, but not restrictively, to a wheel intended for a seed drill element for regulating the working depth of this element and/or for pressing the soil down after this element has passed by.
2. Description of the Related Art
In agricultural machinery of this type a ground working tool such as a ploughshare, a disc or a tooth creates a furrow in which the grains or seeds are buried, the furrow then being closed off to allow the grains or seeds to germinate.
These agricultural machines are drawn by a tractor and are generally of the trailed or semi-trailed type.
The wheel that is fitted to the seed drill serves primarily as a depth control wheel for controlling the working depth of the seed drill. However, it may also serve to press down the soil to close off the furrow in which the grains or seeds have been deposited.
In some machines, these wheels act only as a depth control wheel, while in others they act only as pressing wheels. However, these wheels may also perform a double function of depth control and pressing.
A wheel of this kind may be arranged in front of the tool or behind the tool relative to the direction of travel of the machine.
In every case, these wheels are subjected to difficult working conditions in view of the fact that the machine often moves forward at a speed of the order of 15 to 20 km/h on open fields, i.e. on irregular and sometimes bumpy terrain. They are also subject to considerable stresses, particularly when the machine is banking or performing half-turns.
Moreover, when the wheel travels over wet or sticky ground, wet soil is liable to stick to the wheel, preventing it from fulfilling its functions correctly.
The design of such wheels is therefore particularly tricky.
The most widely adopted solution is a wheel comprising a conventional inflated tire mounted about a conventional rim. For optimum operation, the tire must be inflated to the correct pressure, with the result that the tire thus obtained is prone to stresses and lack of flexibility. It therefore has a tendency to accumulate soil when it travels over wet ground.
Wheels are also known which are fitted with special tires, particularly of the semi-hollow type. Thus, the Applicant markets a wheel comprising a rim formed by a hub surrounded by a peripheral seat having a peripheral slot, as well as a tire of the semi-hollow type comprising a casing having an uninflated inner volume, said casing comprising an inner wall adapted to surround the peripheral seat and provided with a retaining bead adapted to engage in the peripheral slot, as well as a convex outer wall forming the tread of the tire.
The outer wall of the rim is generally cylindrical, as is the inner wall of the casing.
The wheel in this second solution is generally satisfactory, but there is a need to improve performance still further, notably for travelling over difficult terrain, such as sloping or banked terrain or wet and sticky ground.
The invention sets out in particular to provide a solution to this problem.